First off I'm 22 which I believe puts me in the perfect position to have experienced the golden age of videogames. DOS->Windows Vista, NES->Wii. The first FPS I ever played was Doom 2. When my grandparents were buying a computer "an IBM clone" we went to a computer show where I was granted the opportunity to pick out any game I wanted.
Doom 2 plus a Simpsons mod disc won. I was 10 at the time and this game was pretty scary, probably not rated for 10 year olds. I cheated my way through the game and although I found the level design creatures and game mechanics interesting I was never very good at it. There were multiplayer options but I never got a chance to use them so I just ran around invincible killing everything in sight. From memory for the nostalgic: IDDQD, IDKFA, IDCLIP.
Fast forward a couple of years and dozens of games later and I went to a friends house who was playing his nintendo 64 in his parents bedroom. He was playing a game I'd never heard of called Goldeneye 007. And he handed me a controller so we could play against one another. I was happy to get a chance to play a new videogame but I wasn't aware of the pain I was in for.
In match after match he slaughtered me mercilessly. In a game with small but confusing boards, limited spawn locations and complex controls (for its day) I was severely outmatched. I remember playing the complex and having his sneaking through those crouching holes and blowing me away without me even knowing where he was. After about an hour his friend showed up to play with us, great I thought now I will have some time to breathe. Wrong again, apparently this friend had the game at his house to and the bastards would team up on me to deal out the punishment rather than facing each other.
No matter which set of choices I was killed again and again until finally...

Proximity Mines. (Yes I know this is a remote mine, google failed me.) These weapons were the great equalizer where for once the hunted could start setting traps. I would run through the boards putting mines around every corner, under the staircases and in general where they'd be most difficult to see. The friends (read: bastards) would go straight for the machine guns in an attempt to get the direct kill but I would line the halls with mines and hole up in places such as the bathroom of the facility. Eventually I became so good with these tactics that they refused to play proximity mines anymore.
After that I learned to adjust my skills for use with remote mines I perfected the throw and detonate maneuver to create a firewall surrounding my victim. Of course my opponents would use the mines themselves but this is what gave me the opportunity to work slowly with the zoom and aiming to practice shooting mines lying on the ground or attached to walls, eventually becoming quick and accurate enough to hold my own in straight out fire fights.
Sure it took a while and I still got my ass kicked plenty the confidence I gained from those cheap proximity mine kills are what enabled me to keep playing and learn to compete. Proximity Mines in Goldeneye 007 are how I learned not to suck at multiplayer first person shooters. How about you?